Redundantly locked fluid coupling

ABSTRACT

A redundant locking fluid coupling has a first coupling element including a coupling nut and a second coupling element including an outer ring biased towards the sealing end, such as by a coil spring. The coupling nut and outer ring include circumferential ends that are engaged when the coupling nut is tightened on the second coupling element inner member. Rotation of the coupling nut in a loosening direction is prevented by ratcheting teeth, or, in an alternative embodiment, complimentary sawtooth teeth, in the circumferential surfaces of the coupling nut and outer ring. Loosening of the coupling nut may be accomplished by sides of a wrench engaging a wrench lead in chamfer forcing axial movement of the outer ring to disengage the ratcheting teeth, or in the alternative embodiment, loosening torque being sufficient to overcome the thread torque and the increased frictional force across the complementary sawtooth teeth.

The U.S. Government has rights in this invention pursuant to ContractNo. F33657-83C-0281 awarded by the Department of the Air Force.

FIELD OF THE INVENTION

This invention relates to fluid couplings and, more particularly, to acoupling for fluid lines including coupling elements which are subjectto environmentally induced loosening and are therefore redundantlylocked together.

BACKGROUND OF THE INVENTION

Coupling systems for interconnecting lines, such as electric lines orfluid conveying lines, must provide reliable service even in adverseoperating conditions. For example, the couplings for fluid linesassociated with the hydraulic or other systems of aircraft are subjectedto vibration, temperature extremes, axial loading and a variety of otherdifficult operating conditions. Loosening of such couplings in operationcould be catastrophic.

Fluid couplings typically comprise a coupling element with a seat and asecond coupling element with a mating surface that are joined togetherby a coupling nut on one of the elements being threaded onto threads onthe other element and tightened to force the coupling seat and matingsurface together to achieve a fluid tight seal. Thread torque isconventionally used as a measure of whether an appropriate compressionof the sealing surfaces to achieve a fluid tight seal has been reachedand also as a measure that the threaded surfaces are sufficientlyengaged to prevent loosening. Because of the vibration, temperaturecycling, axial loading, and other operating conditions of aircraft,threaded connections that have been adequately "torqued" can oftenloosen after a period of time. In the case of a fluid coupling, evenslight loosening will result in the coupling no longer providing thenecessary fluid-tight connection. Coupling nuts in aircraft applicationshave conventionally been adapted to accommodate lockwire as a means ofpreventing rotation of the torque coupling nut in a loosening direction.Use of lockwire, however, presents problems in maintainability due tothe time necessary for installation and accessibility to the coupling.

SUMMARY OF THE INVENTION

In accordance with the present invention, it is desirable to provide asimple and reliable coupling system that will enable a fluid coupling tobe redundantly locked against loosening in an aircraft environment,including vibration, temperature cycling, and axial loading. It is alsodesirable that the coupling provide a redundant locking system, theprimary locking feature being torque friction of the coupling threads.

Redundant locking of a coupling is achieved by a coupling having twocoupling elements. The first coupling element includes an inner memberhaving a seat for sealing the fluid connection and a coupling nut havinginternal threads for threadingly engaging the second coupling element toachieve the desired thread torque. The second coupling element has anend with a sealing portion to fit into the seat of the first couplingelement, a threaded portion complementary to the coupling nut, andbiasing means, such as a coil spring, biasing an outer ring towards thesealing end such. Accordingly, when the coupling is assembled and thecoupling nut is threaded onto the second element, surfaces oncircumferential ends of the coupling nut and the outer ring will becomeengaged, the surfaces being formed so as to allow rotation of thecoupling nut in a tightening direction but to inhibit rotation of thecoupling nut in a loosening direction. In a preferred embodiment, thecircumferential surfaces may include ratcheting teeth whereby rotationin the loosening direction is prevented unless the teeth are disengaged.

In another embodiment, the circumferential end surfaces of the couplingnut and outer ring comprise complementary saw-tooth teeth such thatrotating the coupling nut in a loosening direction is inhibited, inaddition to thread torque, by the circumferential friction from thenormal force of the spring loaded teeth. The additional force to beovercome is determined by the angle of inclination of the saw-toothsurfaces in concert with the spring load.

Disassembly of the coupling may be accomplished by compressing thespring, allowing sufficient axial movement of the outer ring away fromthe coupling nut to permit the coupling nut to be rotated in a looseningdirection. This axial movement may be accomplished either by directlycompressing the outer ring to provide total clearance of the teeth, asis necessary with ratcheting teeth, or simply by providing asufficiently high loosening torque to overcome the circumferentialfrictional force in addition to the thread torque in a saw-tooth typearrangement.

DESCRIPTION OF THE DRAWINGS

The structural operation and the advantages of the presently preferredembodiments of this invention will become further apparent uponconsideration of the following description taken in conjunction with theaccompanying drawings wherein:

FIG. 1 is an illustration of a cutaway view in partial cross section ofcoupling elements prior to engagement with one another showing oneembodiment of the invention;

FIGURE 1A is an illustration of a cross-sectional view along lines1A--1A of FIG. 1;

FIG. 2 is an illustration of a cross-sectional view along lines 2--2 ofFIG. 1;

FIG. 3 is an illustration of a cutaway view in partial cross section ofthe assembled embodiment of FIG. 1;

FIG. 4 is an illustration of a cutaway view in partial cross section ofcoupling elements in a second embodiment of the invention prior toengagement with one another; and

FIG. 4A is an illustration of an enlarged section of coupling teeth ofFIG. 4;

FIG. 5 is an illustration of a cutaway view in partial cross section ofthe assembled embodiment of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

Like reference numerals have been used to designate like orcorresponding parts throughout the several views.

Referring now to FIG. 1, a cutaway view in partial cross section of anunassembled coupling 10 having a longitudinal axis 12 and comprising afirst coupling element 14 and a second coupling element 40. For purposesof the present discussion, the coupling device 10 is illustrated for usein connection with fluid lines 17 and 43 which convey liquid or gaseousfluids, although it is contemplated that the coupling device 10 could beemployed in essentially any application requiring a joint between twoconduits or lines of a given type. It is also contemplated that firstand second coupling element inner members 16 and 42, respectively, couldbe at least partially formed integrally with fluid lines 17 and 43,respectively.

First coupling element 14 comprises an inner member 16 which may beformed integrally with or fixedly attached, such as by welding, to fluidline 17. The inner member 16 has an outer surface 18 and a first end 20including a seat 22. An annular surface 24 extends outwardly from thefirst coupling element inner member 16 to engage coupling nut 26 inwardextending flange 34 for tightening the coupling. Coupling nut 26includes a threaded internal surface 28 and a first end 30. Coupling nut26, in this preferred embodiment, includes means for inhibitingloosening of the coupling by way of four circumferentially spacedratchet teeth 32 extending axially from first end 30. First end 30 alsohas a annular surface 31 extending radially outward and wrench flats 36.First coupling element inner member 16, annular surface 24, and/ormating surface 35 of coupling nut inward extending flange 34 may includea coating such as a thin layer of silver plating or a dry film lubricantto prevent binding of the surfaces 24 and 35 when the couplingexperiences high thread torque and resultant high pressure forces acrosssurfaces 24 and 35.

Second coupling element 40 is shown having inner member 42 which may beformed partly or wholly integrally with, or fixedly attached, such as bywelding, to fluid line 43. Second coupling element inner member 42includes a first end 44 with a sealing portion 46, shown in thisembodiment as a conventional ball nose fitting, and a second portion 48with a threaded external surface 50 having complementary threads tocoupling nut threaded internal surface 28. Second coupling element innermember 42 further includes a section with spline means 49 extending toradially extending surface 45. Inner member 42 also includes groove 47for a split ring or locking ring 68. Second coupling element 40 outermember also includes outer ring 52 with a first end 54 havingcircumferentially continuous axial extending ratchet teeth 56. The outerring 52 also includes spline means 59, which are complementary to innermember spline means 49, for circumferentially fixing the location of theouter ring. The outer ring also includes wrench flats 51, a cylindricalportion 53 for housing a spring 62, and an inner annular surface 55.Flange 57, including wrench lead in chamfer 80, extends outward fromouter ring 52 such that the wrench flats 51 are between the outwardextending flange 57 and the first end 54.

Biasing means 60 comprise spring 62 located within the cylindricalportion 53 of outer ring 52, spring 62 engages a washer 66 retained inplace by a split ring or a locking ring 68, with the opposite end ofspring 62, engaging an annular surface 55 of outer ring 52 such that thespring 62 is at least lightly compressed, pre-loading outer ring 52.

FIG. 1A shows wrench load in chamfer 80 on outer ring 52 such that aconventional open end wrench can be inserted to engage two oppositelyfacing wrench flats without interference from portions of wrench lead inchamfer 80 on adjacent wrench flats.

FIG. 2 is a cross-sectional view along plane 2--2 of FIG. 1 showingspline means 49 of inner member 42 and the complementary spline means 59of outer ring 52 such that rotation of outer ring 52 with respect innermember 4 is prevented.

As shown in FIGS. 1 and 2, spline means 49 and 59 allow axially slidingmovement of outer ring 52 with respect to inner member 42 while thecircumferential engagement of outer ring 52 is fixed with respect toinner member 42. It is also apparent that the coupling nut of the firstcoupling element is both axially and circumferentially moveable withrespect to first coupling element inner member 16.

FIG. 3 shows the coupling of FIG. 1 with coupling nut 26 threaded ontosecond coupling inner member 42 such that the sealing portion 46 isengaged with first coupling element inner member sealing seat 22.Circumferential ratchet teeth 32 of coupling nut 26 are engaged with thecircumferential ratchet teeth 56 of outer ring 52 an axial length L1,corresponding in this embodiment to the axial length of ratchet teeth32. Consequently, rotation of coupling nut 26 is prevented unless theouter ring 52 is displaced thus allowing rotation of the coupling nut 26in a loosening direction. Such disengagement may be accomplished byinserting a wrench of sufficient width onto wrench flats 51 such that itwill force flange 57, which is on axially moveable outer ring 52, awayfrom annular surface 31 of coupling nut 26 which is axially fixed.Displacement of the outer ring 52 may be accomplished by engaging awrench with wrench flats 51 and compressing spring 62 sufficient torotate coupling nut 26 in a loosening direction.

Assembly of coupling 10, as shown on FIG. 3, is accomplished by axiallyaligning first coupling element 14 with second coupling element 40 andinserting second coupling element inner member sealing portion 46 intofirst coupling inner member seat 22 and engaging coupling nut 26 withsecond coupling element inner member threaded portion 50. A conventionalopen-end wrench should be engaged with second coupling element outerring 52 wrench flats 51 to restrain twisting of second coupling element40 as coupling nut 26 is tightened on the second coupling element innermember 42. A second conventional wrench is used to engage the couplingnut wrench flats 36 and rotate in a tightening direction. The length ofthe coupling nut threaded portion 28 should be as is conventional suchthat sufficient coupling nut threads and second element external threadswill be engaged to provide the necessary torque as determined by theapplication in which the coupling will be installed. The outer ring 52of the second coupling element 40 is preloaded such that prior tocircumferential ratcheting teeth 32 and 56 engaging the spring 62 biasesthe outer ring 52 toward second coupling inner member first end 44, butis stopped where spline means 49 reach end of the inner member splinemeans 59 and the outer ring 52 should be sized such that thecomplementary ratcheting teeth 32 and 56 will permit rotation of thecoupling nut in a tightening direction but will be fully engaged toprevent rotation in a loosening direction when the appropriate torque isreached. As shown in FIG. 3, the assembled coupling will have slightlycompressed the spring 62 from its preloaded position.

Disassembly is the coupling shown in FIG. 3 is accomplished by engaginga wrench with outer ring wrench flats 51 and further compressing spring62 such that outer ring ratchet teeth 56 are totally disengaged fromcoupling nut ratchet teeth 32 and using a wrench to rotate coupling nut26 in a loosening direction. Displacement of the coupling nut may beaccomplished in this preferred embodiment by using a wrench ofsufficient width that engaging the wrench flats 51 of outer ring 52 willcause the sides of the wrench used to further engage the wrench lead-inchamfer 80 and the coupling nut annular surface 31 forcing the outerring 52 away from the coupling nut 26 sufficient for the requiredclearance of ratchet teeth 32 and 56. In order to use a wrench in thismanner, it is necessary to design the wrench lead-in chamfer consideringthe width of the wrench to be used in this application the distancebetween the coupling nut annular surface 31 and the outer ring outwardextending flange 57, denoted in FIG. 3 as L3, the length of the engagedratchet teeth L1 and the width of the wrench to be used. It is necessarythat the width of the wrench is less than L3 so that as the wrench isinserted onto wrench flats 51 it will engage both annular surface 31 andthe wrench lead-in chamfer 80. It is also necessary that the lead-inchamfer distance L2 plus the wrench width be greater than the distanceL3 plus the distance L1 in order for total disengagement of outer ringratchet teeth 56 from coupling nut ratchet teeth 32.

Referring now to FIG. 4, a second embodiment of the invention is shownwith a coupling 11 substantially the same as coupling 10 with thefollowing distinguishing characteristics. Coupling nut 26 of coupling 11has wrench flats 36 proximate first end 20 rather than distal from firstend 20 as in first coupling 10 and first end 20 includescircumferentially continuous sawtooth teeth 33 rather than ratchetingteeth as in coupling 10. Second coupling element 40 of coupling element11 is also different in that wrench flats 76 are affixed to secondcoupling inner member 42 rather than the outer ring 52. Further, toaccommodate assembly of outer ring 52 over second coupling element innermember threaded portion 50, the complementary splines means 49 and 59 oninner member 42 and outer ring 52, respectively, are of a largerdiameter than the threaded portion 50; but, otherwise, are as shown inFIG. 2. Outer ring 52 includes complementary circumferentiallycontinuous sawtooth teeth 58 at first end 54 instead of the ratchetteeth 56 of coupling 10. Assembly of second coupling element 40 ofcoupling 11 is accomplished by inserting spring 62 from first end 44until it is over the spline means portion 49 and then likewiseinstalling the outer ring 52 aligning the outer ring spline means 59with the complementary second coupling element inner member spline means49 and compressing the spring slightly then installing locking ring 70into circumferential groove 71 on second coupling element inner member52, then releasing the outer ring 52 to its spring loaded condition, asshown in FIG. 4.

FIG. 4A shows an enlarged view of the sawtooth teeth 33 of coupling nut26 with α representing the slope or angle of coupling nut surface 83opposing rotation of the coupling nut in a loosening direction and αrepresenting the slope or angle of coupling nut surface 84 opposingrotation of the coupling nut in the tightening direction. Design of thesawtooth arrangement of coupling 11 needs to take into consideration thevibration, axial loading, and other operating conditions that willeffect the necessary normal force across the mating sawtooth surfaces toprevent disengagement of the sawtooth surfaces and/or rotation of thecoupling nut 26 in a loosening direction. This can be accomplished bydetermining the loads necessary to prevent movement of the outer ring 52away from the coupling nut 26 that would allow such disengagementparticularly in a vibration environment. Secondly, the angle α should bedesigned such that it will keep or prevent loosening of the coupling nut26 in such environments, but without too high a safety margin that itwould prevent loosening of coupling nut 26 by application of additionaltorque in a loosening direction without damaging the tooth surfaces orthe coupling nut members. FIG. 5 shows the coupling nut 11 in anassembled configuration. Coupling 11 is assembled by applying a wrenchto wrench surfaces 76 to prevent rotation of the second coupling elementwhile the coupling nut 26 is threaded onto and torqued, by applying asecond wrench to wrench surface 36, onto threaded surfaces 50 of secondcoupling element inner member 42. Installation of the coupling nut 26 isas conventional with a predetermined torque being reached, such thatwhen the coupling nut has reached the necessary tightening torque valuethe sawtooth surfaces are fully engaged and the spring 62 is compressedto provide the required normal force for the desired preloadedcondition.

Disassembly of coupling 11 of FIG. 5 is accomplished by engaging wrenchflats 76 to prevent rotation of second coupling element inner member 42while a second wrench engages wrench flats 36 on coupling nut 26 androtates the coupling nut in a loosening direction. The loosening torquenecessary being that of the thread torque plus the torque necessary toovercome the normal forces on the circumferentially extending sawtooth33 surfaces 82 opposing the rotation in this loosening direction.

The present invention and many of its intended advantages will beunderstood from the foregoing description and it will be apparent thatvarious changes may be made in the form, construction, and arrangementof the parts thereof without departing from the spirit and scope of theinvention or sacrificing its material advantages, the apparatushereinbefore described being preferred and exemplary embodiments.

What is claimed is:
 1. A coupling having a longitudinal axis, saidcoupling comprising:(a) a first coupling element, comprising:(i) aninner member having a first end including a seat; and (ii) a couplingnut having a threaded internal portion, a first end, and an annularsurface extending radially outward substantially adjacent said firstend, said coupling nut being coupled to said first coupling elementinner member such that said coupling nut may move axially andcircumferentially with respect to said first coupling element innermember; and (b) a second coupling element, comprising:(i) an innermember having a first end, a sealing portion adapted to sealingly engagesaid first coupling element inner member seat, a threaded portionadapted to engage said coupling nut threaded internal portion, and axialspline means;wherein said first coupling element and said coupling nuthave coacting abutment means wherein said coupling nut is threadedlyengageable with said second coupling element inner member and rotatablein a tightening direction such that said abutment means engage and saidseat engages said sealing portion to achieve a fluid tight seal; (ii) anouter ring having a first end, at least two wrench flats, an annularflange extending outward substantially adjacent said wrench flats with awrench lead-in chamfer extending axially towards said outer ring firstend, wherein said wrench flats are located between said annular flangeand said first end, and spline means complementary to and axiallyaligned with said second coupling element inner member spline means suchthat said outer ring is coupled to said second coupling element innermember in axially sliding and circumferentially fixed engagement; and(iii) biasing means coupled to said second coupling element inner memberand outer ring urging said second coupling element outer ring axially inthe direction of said second coupling element inner member first end;wherein said first end of said coupling nut and said first end of saidouter ring include intermeshing ratcheting teeth allowing rotation ofsaid coupling nut in a tightening direction and preventing rotation ofsaid coupling nut in a loosening direction by said biasing meansperssing said outer ring ratcheting teeth into interference with saidcoupling nut ratcheting teeth when a fluid tight seal has been achieved;and wherein when a fluid tight seal has been achieved said biasing meansmay be compressed to allow sufficient axial movement of said outer ringaway from said second coupling element inner member first end to permitsaid coupling nut to be rotated in a loosening direction; whereby awrench engaging said outer ring wrench flats would disengage saidratcheting teeth by sides of the wrench engaging said wrench lead-inchamfer and said coupling nut annular surface, forcing said outer ringannular flange away from said coupling nut annular surface, and wouldretain such disengagement to allow rotation of said coupling nut.
 2. Thecoupling of claim 1, wherein said coupling nut further comprises atleast two wrench flats.
 3. A coupling having a longitudinal axis, saidcoupling comprising:(a) a first coupling element, comprising:(i) aninner member having a first end including a seat; and (ii) a couplingnut having a threaded internal portion, a first end, said coupling nutbeing coupled to said first coupling element inner member such that saidcoupling nut may move axially and circumferentially with respect to saidfirst coupling element inner member; and (b) a second coupling element,comprising:(i) an inner member having a first end, a sealing portionadapted to sealingly engage said first coupling element inner memberseat, a threaded portion adapted to engage said coupling nut threadedinternal portion, and axial spline means;wherein said first couplingelement and said coupling nut having coating abutment means wherein saidcoupling nut is threadedly engageable with said second coupling elementinner member and rotatable in a tightening direction such that saidabutment means engage and said seat engages said sealing portion toachieve a fluid tight seal; (ii) an outer ring having a first end andspline means complementary to and axially aligned with said secondcoupling element inner member spline means such that said outer ring iscoupled to said second coupling element inner member in axially slidingand circumferentially fixed engagement; and (iii) biasing means coupledto said second coupling element inner member and outer ring urging saidsecond coupling element outer ring axially in the direction of saidsecond coupling element inner member first end; wherein said first endof said coupling nut and said first end of said outer ring includecomplementary sawtooth teeth, said coupling nut sawtooth teeth havingsurfaces with a slope opposing rotation of the coupling nut in atightening direction less than a slope with an acute angle opposingrotation of the coupling nut in a loosening direction; whereby rotatingof said coupling nut in the loosening direction is inhibited by saidbiasing means pressing said outer ring sawtooth teeth into engagementwith said coupling nut sawtooth teeth increasing frictional forcesbetween mating sawtooth teeth surfaces.